Metal-Free Visible-Light-Induced Trifluoromethylation Reactions

Abstract

Visible-light-induced trifluoromethylation reactions of alkenes with CF3I in the presence of Nile red, which acted as an organic photosensitizer, have been developed. Compared to trifluoromethylations with transition-metal-based photosensitizers like Ru and Ir complexes, the use of Nile red made this process more environmentally benign, not only by avoiding issues associated with metal residues, but also by allowing the use of low-energy photons (yellow LEDs) owing to its light absorbance at long wavelengths (440-600nm). In the process, trifluoromethylated alkene and trifluoromethylated iodoalkane products were selectively synthesized by controlling the reaction conditions. In particular, the base employed significantly affected the selectivity of the process. The iodotrifluoromethylation of alkynes and the trifluoromethylation of N-heterocycles also proceeded well using Nile red. Furthermore, it was found that a (CF3)-C-. radical could be generated in the absence of Nile red under a higher photon energy by visible-light-induced electron transfer between tertiary amines and CF3I, despite the lower reactivity.